Synthesis of Molybdenum- and Vanadium-Containing Mixed Oxides in Polymer–Salt Systems

Rare-earth alkaline-earth mixed oxides containing transition metals (Mo, V) were prepared via pyrolysis in polymer–salt systems. The products were characterized by thermal analysis, resistance measurements, dilatometry, optical microscopy, and x-ray diffraction. The introduction of polyvinyl alcohol into the system containing lanthanum or strontium nitrate and ammonium molybdate was found to have a significant effect on the thermal decomposition process, testifying to changes in the bonding configurations of the constituent components in the systems studied, capable of forming stable gels, which are then used as precursors to synthesize oxide materials. The temperatures of different stages of dehydration were shown to be lower in the polymer-containing systems. The effect of solution acidity was assessed by examining thermal decomposition in systems containing a polymer and Mo or W salts and acidified with nitric acid. The reaction of nitrates (oxidants) with the polymer was accompanied by an exotherm at 170°C, corresponding to the melting of ammonium nitrate, resulting from an exchange reaction. The exothermic reaction was found to reduce the decomposition temperatures of the salts involved. The use of polymer–salt systems allowed the mixed oxides SrMoO₄ and La₂(MoO₄)₃ to be synthesized at lower temperatures in comparison with the coprecipitation of poorly soluble compounds. The method was also shown to be suitable for preparing perovskite oxides in the La_{1 – x} Sr _x Co_{1 – z} M _z O_{3 ± y} (M = Mo, V) systems.     

Rapid Assessment Testing of Polymer Aluminum Electrolytic Capacitors in Elevated Temperature–Humidity Environments

Aluminum electrolytic capacitors with polymer electrolytes were developed to obtain lower equivalent series resistance (ESR) than that is achievable with liquid electrolytes. Replacement of the liquid electrolyte with a solid conductive polymer also overcomes the propensity of the liquid to evaporate over time, which leads to a reduction in capacitance and an increase in ESR values. However, capacitor manufacturers acknowledge that humidity can degrade the polymer, thereby having an adverse effect on the reliability of polymer aluminum (PA) capacitors. In the current study, surface mount and thru-hole PA capacitors from two different manufacturers were subjected to highly accelerated stress testing (110 °C, 85% RH) and elevated temperature–humidity (85 °C, 85% RH) conditions for rapid assessment. The polymer electrolyte in the capacitors was poly(3,4-ethylenedioxythiophene). Failure analysis was performed to determine the observed failure modes and the underlying failure mechanisms. The dominant failure modes observed were an increase in leakage current and an increase in ESR.     

Potential Applications of Polymer Microchips in Pharmaceuticals

Some of the most recent development in polymer based microchips have been reviewed. Different methods used in fabricating ploymer microchips are introduced. The inportance and applications of the ploymer microchip in pharmaceutical and other areas are discussed. Finally, the potential problems and development areas in polymer microchip technology are also addressed.     

Polymer–ITO nanocomposite template for the optoelectronic application

Polymer–ITO (PI) nanocomposite templates with various ITO concentrations have been fabricated by electrospinning. These templates look like a mat with tangled nanofibers, and are optically transparent (85–90%) in the visible region of the solar spectrum (400–700 nm). The electronic properties of those transparent films were studied. The highest conductivity achieved is 1.04 × 10³ S cm⁻¹. The promising optoelectronic properties present the great promise of PI nanocomposites to be the top layer of the next generation flexible photo devices, like solar cells and light emitting diodes (LED).     

Polymer matrix–clay interaction mediated mechanism of electrical transport in exfoliated and intercalated polymer nanocomposites

We report significant results on charge transport phenomena in the exfoliated and intercalated phase of polymer nanocomposite (PNC). X-ray diffraction and transmission electron microscopy results have provided convincing evidence of exfoliation at lower clay loading (x < 5 wt%) and intercalation at higher clay loading (x > 5 wt%) in the PNC. Fourier transform infrared (FTIR) spectrum indicated lowering of anion symmetry from O_h to C_4ν/C_2ν/C_3ν (depending on mode of cation interaction with counter ion). Substantial jump in electrical conductivity (~110 times) at room temperature has occurred on nanocomposite formation in sharp contrast to that of the polymer salt (PS) complex film. Large conductivity enhancement (10⁻³ S cm⁻¹) is attributed to clay-induced interaction with PS matrix whose origin lies in polymer–ion, ion–ion, ion–clay, and polymer–ion–clay interaction evidenced in the FTIR results. An excellent correlation of conductivity with fraction of free anion and polymer glass-transition temperature agrees well with conductivity enhancement at specific clay loading. A model for charge transport phenomena is proposed to explain clay-induced ion dynamics. The conceptual basis of the model seems consistent with experimental results.     

Rheology–Structure Relationship of Polymer/Layered Silicate Hybrids

Linear and non-linear rheology of polymer/layered silicate hybrids(nanocomposites) of organically modified smectite clay in poly(methylmethacrylate) (PMMA) were studied in oscillatory shear and elongationflow for understanding the relation between rheology and structure inthe lights of time-dependent phenomena. Various rules for the linearviscoelastic response were proved by a comparison of the theoreticalpredictions with the experimental data at the low amplitude oscillatoryshear. Time-temperature superposition principal, as well as the relationbetween the relaxation time spectrum and the linear functions, asrelaxation modulus G(t) and elongation viscosity _E (t) were verified.Relaxation spectrum is shifted towards the longer relaxation time scalesfor 10 and 15 wt% SPN/PMMA hybrids, if compared with that of thematrix PMMA. Both the large-amplitude oscillatory shear and the fastelongation produced much stronger non-linear effects of hybrids than thatof pure PMMA. It is proposed that, the non-linear damping of hybridsunder step strain is a result of the strain-induced alignment of themultilayered clay domains in a shear flow field. Moreover, theretardation of the polymer relaxation of hybrids probably gives rise tothe strain-hardening properties under fast elongation. Highly orientedand elongated multilayered domain structure of hybrids in an elongationflow field has been proposed as a microstructural origin of both strainhardening and birefringence.     

Statistics of Polymer‐Chain Conformations in the Intrinsic Coordinate System

The statistics of polymerchain conformations in the intrinsic coordinate system, the directions of whose axes are determined by the anisotropy of a polymer coil at certain instantaneous distribution of the conformations, is considered. It is shown that even for an absolutely flexible polymer chain the shape of the coil in the intrinsic coordinate system is anisotropic. Full distribution functions of the chain links in space are constructed for both the absolutely flexible linear polymer and the linear polymer chain which possesses finite flexural rigidity, and degrees of anisotropy of these macromolecules are calculated.     

Polymer–ceramic conversion of a highly branched liquid polycarbosilane for SiC-based ceramics

Liquid polycarbosilane (LPCS) with a highly branched structure was characterized by fourier-transform infrared spectrometry (FT-IR) and ¹H, ¹³C, ²⁹Si nuclear magnetic resonance spectrometry (NMR). The LPCS was then cured and pyrolysized up to 1,600 °C under flowing argon. The structural evolution process was studied by thermogravimetric analysis and differential scanning calorimetry (TG-DSC), FT-IR, and X-ray diffraction (XRD). Hydrosilylation, dehydrocoupling, and polymerization cross-linking reactions between Si–H and C=C groups occurred at low temperatures, which mainly accounted for the high ceramic yield (70%) up to 1,400 °C. The organic groups gradually decomposed and the structure rearranged at high temperatures. The FT-IR analysis revealed that Si–CH₂–Si chains, the backbone of original polymer, can be retained up to 1,200 °C. At temperatures higher than 1,200 °C, the Si–CH₂–Si chains broke down and crystalline SiC began to form. The final crystalline products were β-SiC and a small amount of carbon.     

Polymer–clay nanocomposites via chemical grafting of polyacrylonitrile onto cloisite 20A

The synthesis and characterization of polyacrylonitrile (PAN) nanocomposites through grafting the polymer onto organophilic montmorillonite have been reported. Cloisite 20A reacted with vinyltrichlorosilane to replace the edge hydroxyl groups of the clay with a vinyl moiety. Because the reaction liberates HCl, it was performed in the presence of sodium hydrogen carbonate to prevent the exchange of quaternary alkylammonium cations with H^?+? ions. Only the silanol groups on the edge of the clay reacted with vinyltrichlorosilane. The radical polymerization of the product with acrylonitrile (AN) as a vinyl monomer leads to chemical grafting of polyacrylonitrile onto montmorillonite surface. The homopolymer formed during polymerization was separated from the grafted organoclay by Soxhlet extraction. Chemical grafting of the polymer onto Cloisite 20A was confirmed by infrared spectroscopy. The prepared nanocomposite materials and grafted nanoparticles were studied by XRD and TEM. Exfoliated nanocomposites were obtained for 0·5–7 wt% clay content. The nanocomposites were studied by thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMTA).     

The Fulde–Ferrell–Larkin–Ovchinnikov State in Pnictides

We present experimental results on crosstalk of non-electrical origin between high frequency quartz tuning forks immersed in the same volume of helium gas, liquid or superfluid. We compare these results with various observations of other groups and propose an explanation of this puzzling phenomenon. To the best of our knowledge, notable crosstalk has only been observed in superfluid helium both in the two-fluid regime and at very low temperatures, but was rarely seen to behave in a systematic way. We demonstrate some of its most significant properties—amplitude dependence within a short time span, long-term temporal instability, effects of the geometry of the setup and of obstacles placed between the tuning forks. Although the results are not fully understood, as the most likely explanation, we ascribe the observations to the coupling of tuning forks to standing acoustic modes inside the experimental volume, emphasizing the importance of second sound for understanding the observations at temperatures within the two-fluid regime (1 K<T<2.17 K). Finally, we suggest simple precautions leading to suppression of excessive acoustic crosstalk between oscillating objects in He II.     

Polymer film formation in C2F6H2 discharges

Thin fluoropolymer films deposited in an r.f. discharge fed with C₂F₆H₂ mixtures were studied. The effect of the electrical characteristics, the substrate temperature and the feed composition on both the chemical structure of the film and on the growth mechanism were analysed.It was found, in particular, that the structure of the film is affected by the H₂ concentration in the feed and by the discharge voltage and current values and that the polymerization rate decreases with temperature after a threshold.     

Heterogeneous Phase Equilibria in Rare Earth–Mn–O Systems in Air

The phase relations in rare earth–Mn–O systems in air are considered. Most of the phase diagrams of these systems fall into two distinct groups: R"–Mn–O (R" = Y, Ho–Lu) and R"–Mn–O (R" = Pr, Nd, Sm–Dy). In addition, the Sc–Mn–O, La–Mn–O, and Ce–Mn–O systems have phase-diagram features of their own. The Ce–Mn–O system contains no ternary oxides or solid solutions: there are only mixtures of cerium and manganese oxides. The Sc–Mn–O system has phase-diagram features in common with both the R"–Mn–O and M–Mn–O (M = Mg, Al, 3d transition metal) systems. The La–Mn–O phase diagram can be thought of as a degenerate diagram of the R"–Mn–O group, since LaMn₂O₅ exists at oxygen pressures higher than atmospheric pressure. The R"–Mn–O and R"–Mn–O systems contain two chemical compounds, RMnO₃ and RMn₂O₅, but differ in the crystal structure of RMnO₃: hexagonal in the R" group and orthorhombic perovskite-like in the R" group. A key role in determining the structure of RMnO₃ is played by the size factor. In both groups, the RMn₂O₅ compounds dissociate in air by the reaction \({\text{RMn}}_{\text{2}} {\text{O}}_{\text{5}} {\text{ = RMnO}}_{\text{3}} + \frac{1}{3}{\text{RMn}}_{\text{3}} {\text{O}}_{\text{4}} + \frac{1}{3}{\text{O}}_{\text{2}} \). The dissociation temperature of RMn₂O₅ is shown to correlate with the atomic number of R, the total number of 4f electrons, the number of unpaired 4f electrons, and the ionic radius of R³⁺.     

New trends in V–P–O solids

On the basis of the industrial interest of the oxovanadium phosphate catalysts, current research effort in this field is focused mainly on the development of synthetic strategies directed towards obtaining open-framework materials. There is a growing body of work describing preparations using hydrothermal procedures under a diversity of conditions. A great number of new solids, whose nets range from lamellar arrays to micro- and mesostructured organizations, has been prepared in last years. In this context, the applicability of concepts and procedures from the zeolites chemistry to systems involving transition elements is critically analyzed.     

Joule–Thomson Inversion in Vapor–Liquid–Solid Solution Systems

Solid phase precipitation can greatly affect thermal effects in isenthalpic expansions; wax precipitation may occur in natural hydrocarbon systems in the range of operating conditions, the wax appearance temperature being significantly higher (as high as 350 K) for hyperbaric fluids. Recently, methods for calculating the Joule–Thomson inversion curve (JTIC) for two-phase mixtures, and for three-phase vapor–liquid–multisolid systems have been proposed. In this study, an approach for calculating the JTIC for the vapor–liquid–solid solution systems is presented. The JTIC is located by tracking extrema and angular points of enthalpy departure variations versus pressure at isothermal conditions. The proposed method is applied to several complex synthetic and naturally occurring hydrocarbon systems. The JTIC can exhibit several distinct branches (which may lie within two- or three-phase regions or follow phase boundaries), multiple inversion temperatures at fixed pressure, as well as multiple inversion pressures at given temperature.     

Phase Relations in the Reduction of Solid Solutions in the Co–Mn–Ti–O System

The hydrogen reduction of spinel solid solutions in the Co–Mn–Ti–O system was investigated by a static method. Six phase regions were identified in which the gas phase is in equilibrium with various combinations of -Co, TiO₂ (rutile), and solid solutions of variable composition: Co _A Mn _B Ti_{3 – A – B} O₄ (spinel), Co _m Mn_{2 – m} TiO₄ (spinel), Co _N Mn_{1 – N} TiO₃ (ilmenite), and Co _n Mn_{1 – n} O (NaCl). The equilibrium compositions of the solid solutions and the corresponding oxygen partial pressures were determined, and the general trends of the reduction of spinel solid solutions in the Co–Mn–Ti–O system were established.     

Measurements of the Thermal Diffusivity Tensor of Polymer–Carbon Fiber Composites by Photothermal Methods

The thermal diffusivity tensor of a polymer–carbon fiber composite with unidirectionally distributed fibers has been measured using a modulated photothermal mirage device. The thermal diffusivity along the fibers is k =6.0±0.5 mm²·s^–1, that perpendicular to the fibers is k =0.35±0.05 mm²·s^–1, and that perpendicular to the sample surface is k _z=0.40±0.15 mm²·s^–1. These results have been confirmed by independent measurements on the sample by other laboratories using three other different photothermal techniques. A previous claim on anomalous results found on this sample (k <k and high thermal diffusivities) can be explained by the inappropriate use of the frequency range. We have also found that there is not perfect thermal contact between the fibers and the matrix, which can be characterized by the thermal contact resistance of R _th=(9±2)×10^–6m²·K·W^–1.     

p–T–x Phase Equilibria in the Cd–Zn–Te System

The p–T–x–y phase equilibria in the Cd–Zn–Te system are analyzed. The p–T and T–x–yprojections of the p–T–x–y phase diagram and a T–x–y isobar (for pressures at which Cd_1–x Zn _x Te_{1 ±} solid solutions sublime congruently in terms of Te) are mapped out. The key features of the sublimation behavior of the solid solution are examined. The p–T projection is studied by static vapor pressure measurements at temperatures from 700 to 1300 K and pressures of up to 101.3 kPa. The p–T sections of the phase diagram are constructed for x = 0.05, 0.10, 0.15, 0.25, 0.50, 0.75, 0.90, and 1. The solid solution containing 35 mol % ZnTe is found to phase-separate at 473 K.     

A Narrow-Bandgap n-Type Polymer with an Acceptor–Acceptor Backbone Enabling Efficient All-Polymer Solar Cells

Narrow-bandgap polymer semiconductors are essential for advancing the development of organic solar cells. Here, a new narrow-bandgap polymer acceptor L14, featuring an acceptor–acceptor (A–A) type backbone, is synthesized by copolymerizing a dibrominated fused-ring electron acceptor (FREA) with distannylated bithiophene imide. Combining the advantages of both the FREA and the A–A polymer, L14 not only shows a narrow bandgap and high absorption coefficient, but also low-lying frontier molecular orbital (FMO) levels. Such FMO levels yield improved electron transfer character, but unexpectedly, without sacrificing open-circuit voltage (V_oc), which is attributed to a small nonradiative recombination loss (E_loss,nr) of 0.22 eV. Benefiting from the improved photocurrent along with the high fill factor and V_oc, an excellent efficiency of 14.3% is achieved, which is among the highest values for all-polymer solar cells (all-PSCs). The results demonstrate the superiority of narrow-bandgap A–A type polymers for improving all-PSC performance and pave a way toward developing high-performance polymer acceptors for all-PSCs.     

New Cubic Phases in the Li–Na–Sb–Bi System

New compounds with the general formula A _x A"_3-x B _y B"_1-y (A, A" = Li, Na; B, B" = Sb, Bi) were prepared in the system Li–Na–Sb–Bi. Na₃Sb_0.5Bi_0.5has a hexagonal structure (Na₃As type, a= 5.415 Å, c= 9.595 Å), and Li₃Sb_0.5Bi_0.5and Li₂NaSb_0.5Bi_0.5have a cubic structure (BiF₃type, a= 6.645 and 6.772 Å, respectively). The phase transitions of alkali-metal pnictides were studied by in situ x-ray diffraction at room temperature and pressures from 10⁵Pa to 9.0 GPa. Li₃Sb and Na₃Sb were each shown to exist in two polymorphs with hexagonal (Na₃As type) and cubic (BiF₃type) structures. At atmospheric pressure, Li₃Sb undergoes an irreversible – phase transition at 650°C, while Na₃Sb undergoes a reversible transformation into a cubic phase at 2.3 GPa and room temperature.     

Optimizing Concentration of Drag Reducing Polymer in Case of One- and Two-Phase Flow in 90° Copper Elbow

Journal of Failure Analysis and Prevention - The rate of diffusion-controlled corrosion of 90° Copper Elbow by acidified dichromate has been investigated in relation to the following...